For an engine, a valve stem seal assembly cooperates with an engine valve stem to provide lubrication and to contain engine gases within engine inlet and exhaust ports. To accomplish these functions, such a valve stem seal assembly typically includes an elastomeric seal that provides an elastomeric-to-metal seal between the engine elastomeric seal and the engine valve stem.
FIG. 1 illustrates a prior art valve stem seal assembly, which is disclosed in U.S. Pat. No. 6,450,143, having a one-piece cylindrical-shaped foundation seal retainer 128 for supporting a valve stem seal 126. The retainer 128 includes a lower portion 130 and an upper portion 134. The lower portion 130 is separated from the upper portion 134 by a transition area 136. The transition area 136 serves to reduce the inner diameter of the retainer 128 between a lower diameter D1 and an upper diameter D3. The transition area 136 is formed as an inwardly extending radial ledge located on the valve guide 22 where the diameter of the valve guide 22 is reduced from a first diameter 137 to a smaller, second diameter 139.
An inner surface 138 of the transition area 136 engages an upper surface 140 of the first diameter 137 of the valve guide 22. The valve stem seal 126 engages the outer circumference 54 of the valve stem 20 to provide a seal. An outer circumference 158 of the seal 126 is supported by and engages an inner circumference of the upper retainer portion 134. The valve stem seal 126 includes an upper seal 160 and a lower seal 162. The upper seal 160 includes an inner surface 145 that engages an upper surface 147 of the second diameter 139 of the valve guide 22. The retainer lower portion 130 has a valve spring 24 disposed therearound. The valve spring 24 rests on and cooperates with an integral flange 43 to maintain the seal 126 in position on the valve guide 22. Under high pressure conditions, the valve spring 24 tends to prevent the guide 22 from being lifted, which can result in seal failure due to bursting.
Unfortunately, the cylindrical-shaped foundation retainer 128 of the '143 patent has a limited effect in an axial direction by allowing the elastomeric seal 126 to partially axially extrude from the bottom to the top of the seal 126 when pressure is applied under the elastomeric seal 126. Such cylindrical-shaped foundation seal support assemblies only partially solve the problem of leakage in the axial direction into which the elastomeric seal 126 partially extrudes. Consequently, the cylindrical-shaped foundation arrangement has limited strength in the axial direction by allowing the elastomeric seal 126 to shear and partially extrude when pressure is applied under the elastomeric seal 126.
Therefore, what is sought is a valve stem seal assembly whose elastomeric seal does not extrude, thereby providing a low oil metering rate performance and better containment of engine gases in the axial direction, than existing one-piece cylindrical-shaped foundation valve stem seal assemblies.